1. (a) Technical Field
The present invention relates to a radiant heat plate for radiating heat from a battery cell module. More particularly, the present invention relates to a multifunctional radiant heat plate having a sensor function, a vibration control and battery stability control function, and an energy harvest function while effectively radiating heat accumulated in a battery cell and module.
2. (b) Background Art
Generally, local temperature differences and undesired high heat may occur in batteries for electric vehicles due to the heat generated by high-output, high-speed, and repetition of battery charging and discharging. This causes thermal runaway, which hinders the efficiency and stability of batteries. Thermal runaway refers to a condition in which an increase in temperature creates a local environmental change that leads to a further increase in temperature (e.g., a positive temperature feedback loop), and may result from a deficiency in the ability of a battery to effectively radiate and diffuse generated heat to the outside environment.
Lithium ion batteries with a cell working voltage of about 3.6 V or higher have been used as power sources for portable electronics, and also as a power sources for eco-friendly vehicles such as high-power Hybrid Electric Vehicles (HEV) or pure Electric Vehicles (EV) by allowing a plurality of cells to be connected in series to each other. The lithium ion batteries have a working voltage three times higher than that of nickel-cadmium batteries or nickel-metal hybrid batteries, and have a better energy density per unit weight.
Lithium ion batteries can be manufactured in various types. For example, a pouched type of battery cell (e.g., a pouch cell) that has a flexible case is widely used, and because the a pouch cell has flexibility in its case, it has a great deal of formability with respect to its shape.
The pouched type of battery cells includes a battery part and a pouched type of case having a space for receiving the battery part. The battery part includes an anode plate, a separator, and a cathode plate which are sequentially disposed and wound in one direction, or includes a plurality of anode plates, separators, and cathode plates which are stacked in a multi-layered structure.
FIG. 1 is a view illustrating a cell module 10 having a plurality of pouched type cells 11 stacked therein. As shown in FIG. 1, adjacent cells 11 are mutually connected to each other through an electrode part 12. The cells 11 are spaced from each other by a certain interval, e.g., 3 mm or more. This interval serves as a channel space 13 between the cells 11 through which cooling air passes. Cooling air passes through the channel space 13 between cells 11 to allow heat of cells 11 to be discharged to the outside (the arrow of FIG. 1 represents the traveling direction of cooling air).
The pouched type of battery cells may vary in their volume due to intercalation/deintercalation of lithium ions to/from an electrode material during charging/discharging. Also, since damage of the separator may occur due to expansion of the electrode plate in the battery cell, and may generate internal resistance, increase voltage, and reduce final battery capacity, a radiant heat interfacial member (member disposed between battery cells) for dealing with the volume expansion of the battery is needed.
Additionally, when the volume of the cell in a typical battery system increases, a channel space formed between cells in the unit of a battery pack decreases in size, which reduces the ability to cool the battery. Accordingly, heat generation between battery cells due to the temperature rise of adjacent battery cells is accelerated, causing a rapid reduction in battery performance. In addition, when the volume of expansion of the battery cell is severe, the pouched type of case (e.g., formed of a polymer material) may be damaged, resulting in electrolyte and gas leakage from the inside of the battery. Furthermore, since the battery cell module and pack are structured by stacking pouched cells, the volume expansion of the cell or the gas leakage or explosion may directly damage adjacent cells.
Accordingly, in order to achieve a compact battery radiant heat system for improving energy density versus volume, the elasticity and the heat radiation performance of a material capable of dealing with the volume variation of the battery cell needs to be sufficient.
Typical battery cases and housing materials in which 20 to 30 wt % mineral filler, i.e., an incombustible filler is filled in a plastic matrix such as PC+ABS, PA, and PP, have functions such as frame resistance, chemical resistance, insulation characteristics, and durability, however, they have no heat radiation characteristics.
A radiant heat material under development focuses on the reduction of the interfacial reduction and improvement in the heat transfer characteristics through the increase of the contact surface between fillers that are highly filled. Also, in the case of a plastic-based radiant heat composite material, there is a limitation in effectively radiating heat generated in the pouched type of battery due to low heat conduction anisotropy and low heat conductivity.
Also, in a typical air cooling type of a cell module 10, since an air channel (channel space) 13 has to be maintained at a certain interval, e.g., 3 mm or more, the energy density per unit volume is difficult to improve. In other words, since the cells 11 are maintained at a certain interval when the battery cell module 10 having a certain volume is configured, there is a limitation in increasing the number of cells. Also, when the number of cells increases, the volume of the module 10 rapidly increases due to the thickness of cell and the interval between cells.
Thus, there is a need for an improved design for heat radiation of the battery cell module and development of a material optimized to the improved design.
A method of using a radiant heat plate between cells to reduce the size of batteries and improve the cooling effect has been recently proposed. This radiant heat plate has a configuration in which a flexible elastomer polymer material having high heat conduction efficiency is coated on an aluminum plate. This radiant heat plate provides an advantage that can maximize the contact surface with cells using the elasticity of the material. Also, when the radiant heat plate is used, air channels between cells can be omitted, enabling more cells to be disposed in one battery pack, and reducing the size of the battery in the same power. Also, the radiant heat plate shows higher heat radiation performance than existing designs. However, the radiant heat plate provides only a simple heat radiation function. Accordingly, the radiant heat plate needs to be equipped with various subsidiary devices in order to provide the stability of the battery, NVH performance and other performances. This causes an increase in the manufacturing cost and the weight of the battery, and makes it very difficult to provide the desired functions in view of the available space and battery environment.
A high voltage battery is being widely used for various apparatuses requiring high power due to today's environmental issues. It is desirable to provide subsidiary functions such as a vibration control and battery stability control function, a sensor function, and an energy harvest function (energy conversion function) in addition to the heat radiation function, the stability, and the durability to the battery. Thus, in order to solve the above-mentioned limitations, there is a need for the development of a radiant heat material for a battery that can perform various complex functions.